Index: openacs-4/packages/calendar/www/view.tcl
===================================================================
RCS file: /usr/local/cvsroot/openacs-4/packages/calendar/www/view.tcl,v
diff -u -r1.31.2.3 -r1.31.2.4
--- openacs-4/packages/calendar/www/view.tcl	13 May 2016 18:05:48 -0000	1.31.2.3
+++ openacs-4/packages/calendar/www/view.tcl	1 Jun 2016 12:09:59 -0000	1.31.2.4
@@ -11,7 +11,7 @@
     {date ""}
     {sort_by ""}
     {start_date ""}
-    {period_days:integer {[parameter::get -parameter ListView_DefaultPeriodDays -default 31]}}
+    {period_days:integer,notnull {[parameter::get -parameter ListView_DefaultPeriodDays -default 31]}}
 } -validate {
     valid_date -requires { date } {
         if {$date ne "" } {